1. Field of the Invention
The present invention relates to a drive wheel support bearing assembly for rotatably supporting a vehicle wheel of a type used in, for example, an automotive vehicle and, more particularly, to a drive wheel support bearing assembly of a fourth generation type equipped with a sensor, in which a hub axle and a constant velocity universal joint are unitized together.
2. Description of the Prior Art
For safety travel of an automotive vehicle, the wheel support bearing assembly has hitherto been well known in the art, which is equipped with a sensor for detecting the rotational speed of one of automotive wheels. While the automobile traveling safety precaution is generally taken by detecting the rotational speed of a wheel of various parts, it is not sufficient with only the rotational speed of the wheel and, therefore, it is desired to achieve a more stable and more precise vehicle attitude control for safety purpose with the use of other sensor signals.
In view of this, it may be contemplated to achieve the vehicle attitude control based on a load acting on each of the wheels during travel of an automotive vehicle. By way of example, a large load acts on the outside wheels during the cornering, on the wheels on one side during the run along left and right inclined road surfaces or on the front wheels during the braking, and, thus, a varying load acts on the vehicle wheels. Also, even in the case of the uneven live load, the loads acting on those wheels tend to become uneven. For this reason, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels can be controlled beforehand based on results of detection of the loads so that the attitude of the automotive vehicle during the traveling thereof (for example, prevention of a rolling motion during the cornering, prevention of diving of the front wheels during the braking, and prevention of diving of the vehicle wheels brought about by an uneven distribution of live loads) can be accomplished. However, no space for installation of the load sensor for detecting the load acting on the respective vehicle wheel is available and, therefore, the attitude control through the detection of the load can hardly be realized.
Also, in the event in the near future the steer-by-wire is introduced and the system, in which the wheel axle and the steering come not to be coupled mechanically with each other, is increasingly used, information on the road surface comes to be required to transmit to the steering wheel hold by a driver by detecting a wheel axis direction load.
In order to meet those needs hitherto recognized, the provision of a sensor for detecting the load acting on the wheel support bearing assembly has been suggested. (See, for example, the Patent Document 1 quoted below.)
In the wheel support bearing assembly for a vehicle drive wheel, a fourth generation type structure, in which a hub axle 10, a constant velocity universal joint 40 and a bearing unit 20 are unitized, is often employed as shown in FIG. 16. Except for a sensor for detecting the rotational speed of the vehicle wheel that is directly installed in the drive wheel support bearing assembly including the fourth generation type, various sensors including, for example, an acceleration sensor, which are used to secure information useful in the vehicle attitude control, are generally mounted on an upper side of suspension springs that are disposed between the vehicle body structure and the drive wheel support bearing assembly, or on the side of a vehicle body structure on the suspension springs.
Also, a version of the wheel support bearing assembly of the fourth generation type discussed above, has also been suggested, in which a stem portion 45 of an outer coupling member 41 of the constant velocity universal joint 40 has an axially extending center bore defined therein and is, while the stem portion 45 is neatly inserted into an axially extending center bore of the hub axle 10, expanded radially outwardly by use of a crimping tool to fasten the hub axle 10 and the outer coupling member 41 together (See Patent Document 2 quoted below). While some crimping techniques are available for fastening the outer coupling member 41 and the hub axle 10 together, the diametrical expansion and crimping technique referred to above has some advantages in that loosening does little occur in the crimped area and, accordingly, a preload release resulting from a change in dimension between double row raceway surfaces can be prevented and the preload can therefore be maintained in the bearing assembly.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2006-9866
[Patent Document 2] Japanese Laid-open Patent Publication No. 2002-254901
As discussed above, in the drive wheel support bearing assembly, in which the hub axle, the constant velocity universal joint and the bearing unit are unitized, the various sensors for use in the vehicle attitude control are mounted on the side of the vehicle body structure above springs or so-called on a sprung mass side. For this reason, a time lag tends to occur in receiving the information and as a result, an increase of the response of a control system to, for example, a change in status of the road surface has been limited. Also, detailed information on the drive wheel support bearing assembly including, for example, a change in dimension between the double row raceway surfaces, which is associated with the preload and rigidity of the bearing unit, cannot be detected, failing to achieve an accurate vehicle attitude control.
Also, in the case of the above described diametrical expansion and crimping technique, in which the stem portion 45 is radially outwardly expanded so that the hub axle 10 and the constant velocity universal joint 40 can be fastened together, the loosening occurs hardly in the crimped area, and further, displacement in position between the hub axle 10 and the outer coupling member 41 of the constant velocity universal joint 40 occurs hardly. However, even with the diametrical expansion and crimping technique, when an excessive external input such as, for example, ride over a curb is applied, loosening may occur in the crimped area, accompanied by a change in dimension between the double row raceway surfaces, and this may lead to release of the preload. The preload release then leads to earlier peeling of the bearing and reduction in rigidity and, therefore, it is desirable to monitor at all times, the condition in which they are fastened together.